1. Field of the Invention
The present invention relates to a high-pressure fuel pump control device for an internal combustion engine that performs feedback control to adjust a pressure deviation between a target pressure and a fuel pressure in an accumulator, to be zero.
2. Description of the Related Art
In general, an internal combustion engine of a type for directly injecting and supplying fuel into a combustion chamber raises a fuel pressure to a pressure optimum for a combustion state (a target pressure) by pressurizing the fuel supplied to a fuel injection valve with a high-pressure fuel pump.
A high-pressure fuel pump control device for the internal combustion engine of this type calculates a fuel discharge feedback quantity on the basis of a pressure deviation between the target pressure and a fuel pressure in an accumulator detected by a fuel pressure sensor, determines drive timing for a flow control valve on the basis of the fuel discharge feedback quantity, and adjusts a fuel discharge quantity of the high-pressure fuel pump. Accordingly, the fuel pressure in the accumulator is controlled to coincide with the target pressure.
The high-pressure fuel pump control device calculates the fuel discharge feedback quantity used for determination of drive timing of the flow control valve by executing a proportional integral operation or the like based on a pressure deviation between a target pressure set on the basis of an operation state of the internal combustion engine and a fuel pressure in the accumulator detected by the fuel pressure sensor.
Subsequently, the high-pressure fuel pump control device adds up the fuel discharge feedback quantity and a fuel injection quantity of the fuel injected from the fuel injection valve to calculate a target fuel discharge quantity (=fuel discharge feedback quantity+fuel injection quantity) of the high-pressure fuel pump. Further, the high-pressure fuel pump control device converts the target fuel discharge quantity into drive timing for the flow control valve using a drive timing map.
Finally, the high-pressure fuel pump control device drives the flow control valve at the drive timing subjected to the map conversion. Accordingly, a quantity of fuel equivalent to a fuel discharge quantity necessary for causing the fuel pressure in the accumulator to coincide with the target pressure is supplied from the high-pressure fuel pump to the accumulator.
The fuel injection quantity used for calculating the target fuel discharge quantity of the high-pressure fuel pump is a quantity of fuel flowing out from the accumulator when the fuel is injected from the fuel injection valve. The fuel injection quantity is equivalent to a fuel discharge quantity necessary for maintaining the fuel pressure in the accumulator.
The fuel discharge feedback quantity used for calculating the target fuel discharge quantity of the high-pressure fuel pump is equivalent to a fuel discharge quantity necessary for adjusting a pressure deviation between the target pressure and the fuel pressure in the accumulator to be zero. The fuel discharge feedback quantity increases and decreases according to the pressure deviation.
For example, when the pressure deviation is larger than zero (the fuel pressure is lower than the target pressure), since the fuel discharge feedback quantity increases, the fuel discharge quantity of the high-pressure fuel pump increases and the fuel pressure in the accumulator rises.
On the other hand, when the pressure deviation is smaller than zero (the fuel pressure is higher than the target pressure), since the fuel discharge feedback quantity decreases, the fuel discharge quantity of the high-pressure fuel pump decreases and the fuel pressure in the accumulator falls.
In this way, the fuel discharge quantity of the high-pressure pump is subjected to feedback control to adjust the pressure deviation to be zero (make the fuel pressure in the accumulator and the target pressure equal).
When the pressure deviation is larger than zero, it is attempted to raise the fuel pressure in the accumulator to the target pressure by increasing an integral operand in the fuel discharge feedback quantity. However, when a state in which the pressure deviation is larger than zero lasts long, the integral operand increases excessively.
It is known that, when the integral operand increases excessively in this way, a fuel discharge quantity after the fuel pressure in the accumulator has reached the target pressure becomes excessively large, and the fuel pressure in the accumulator rises because it is impossible to maintain the fuel pressure at the target pressure, thereby causing so-called overshoot.
Proposed in view of this is a high-pressure fuel pump control device for an internal combustion engine, which is configured to prohibit update of an integral operand when a fuel discharge quantity of a high-pressure fuel pump rises to a value near a maximum value (see, for example, JP 2001-263144 A).
According to the conventional device described in JP 2001-263144 A, the integral operand is prevented from increasing excessively when a fuel pressure in an accumulator is raised to a target pressure. Thus, the occurrence of overshoot is controlled.
On the other hand, when the pressure deviation is smaller than zero, it is attempted to decrease the fuel pressure in the accumulator to the target pressure by reducing the integral operand in the fuel discharge feedback quantity. However, when a state in which the pressure deviation is smaller than zero lasts long, the integral operand decreases excessively.
It is known that, when the integral operand decreases excessively, a fuel discharge quantity after the fuel pressure in the accumulator has reached the target pressure becomes excessively small, and the fuel pressure falls because it is impossible to maintain the fuel pressure in the accumulator at the target pressure, thereby causing so-called undershoot.
Thus, proposed is a high-pressure fuel pump control device for an internal combustion engine, which is configured to prohibit update of an integral operand when a fuel pressure in an accumulator is higher than a target pressure by a quantity equal to or larger than a predetermined quantity (see, for example, JP 6-137199 A).
According to the conventional device described in JP 6-137199 A, the integral operand is prevented from decreasing excessively when the fuel pressure in the accumulator is decreased to the target pressure. Thus, the occurrence of undershoot is controlled.
In the conventional high-pressure fuel pump control device for an internal combustion engine, for example, in the case of JP 2001-263144 A, the integral operand is prevented from increasing excessively by mistake when the state in which the pressure deviation is larger than zero (the fuel pressure is lower than the target pressure) lasts long. Thus, it is possible to control the occurrence of overshoot after the fuel pressure in the accumulator has reached the target pressure. However, the integral operand continues to increase without update thereof being prohibited until it is judged that the fuel discharge quantity of the high-pressure fuel pump has reached the value near the maximum value. Thus, when the fuel discharge quantity does not reach the value near the maximum value or when it takes long until the fuel discharge quantity reaches the value near the maximum value, prohibition of the increase in the integral operand is delayed, a sufficient effect for controlling overshoot is not obtained, and a combustion state or an exhaust gas is deteriorated.
In the case of JP 6-137199 A, the integral operand is prevented from decreasing excessively when the state in which the pressure deviation is smaller than zero (the fuel pressure is higher than the target pressure) lasts long. Thus, it is possible to control the occurrence of undershoot after the fuel pressure in the accumulator has reached the target pressure. However, the integral operand continues to decrease without update thereof being prohibited until it is judged that the fuel pressure in the accumulator has reached a value higher than the target value by a quantity equal to or larger than the predetermined quantity. Thus, when the fuel pressure in the accumulator does not reach the value higher than the target value by the quantity equal to or larger than the predetermined quantity or when it takes long until the fuel pressure in the accumulator reaches the value higher than the target value by the quantity equal to or larger than the predetermined quantity, prohibition of the decrease in the integral operand is delayed, a sufficient effect for controlling overshoot is not obtained, and a combustion state or an exhaust gas is deteriorated.
Moreover, in both the cases of JP 2001-263144 A and JP 6-137199 A, when a value of the integral operand at a point when update of the integral operand is prohibited is a value inappropriate for an operation state at the time when the update of the integral operand is resumed, overshoot or undershoot of the fuel pressure occurs when the update of the integral operand is resumed. This causes deterioration in a combustion state or an exhaust gas.